Pipes for transporting fluids, particularly those used in the oil and gas industry, that are subject to defects such as corrosion, mill defects, stress corrosion cracking, and hydrogen induced cracking. Known methods of dealing with such defective pipes are described in the background of applicant's Canadian patent 2,164,011 and U.S. Pat. No. 5,722,463, and are briefly reviewed herein.
Pipe wall defects have the potential to cause failures during operation, and the usual methods of preventing such failures are either to remove the defect by cutting out a section of the pipe, or by significantly reducing the internal pressure in the pipe prior to either welding a pressure containing sleeve onto the pipe or by applying a mechanically tightened or fibre glass sleeve to the pipe. A disadvantage of these prior methods is that they may require pipe system shut downs and a resultant loss of throughput of product in the pipe. For instance, shut downs are typically required where sleeves are welded directly to a pipe. Such methods also involve occupational hazards, potential metallurgical failures, and costly expenditures. Another disadvantage is that prior art sleeves, if installed while the pipe is under operating pressures, can loosen and separate from the pipe if the operating pressure later drops for any reason. As a result, prior art sleeves require frequent maintenance, repair and replacement, which adds significantly to the operating costs of a pipe.
The sleeve assembly described in applicant's Canadian and US patents addresses the limitations and disadvantages of the prior art by not being welded to the pipe, and being capable of installation whether the pipe is pressurized (i.e. operating) or not. If installed while the pipe is pressurized, the sleeve remains firmly secured to the pipe upon depressurization or shut down, and is relatively quickly and economically installed. However, these types of prior art sleeve assemblies are directed to repairing pipes with anomalies or corrosion which affect or extend radially through only a portion of the pipe wall, namely partially corroded or unperforated pipes.
What is desired, however, is a pipe reinforcement with an improved external sleeve for repairing not only unperforated pipes that transport fluids under pressure, but also perforated pipes (i.e. where pipe wall is corroded or cracked between the interior and exterior surfaces). Preferrably the improved external sleeve should provide greater compressive forces onto the underlying pipe, particularly onto larger diameter pipes (30 inches/76 cm or more), for a given amount of heat input, but is equally effective on smaller diameter pipes (under 30 in/76 cm). The pipe reinforcement should include an improved method of clamping such improved external sleeve on a pipe, including larger diameter pipes. The clamping method should include screw jacks that are mountable onto the sleeves for holding the sleeves on the pipe during the sleeve mounting process, which may be removed from the sleeves when finishing the sleeve mounting process, and which omit the use of a chain assembly extending circumferentially about the pipe.